JP3006155B2 - Liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a super twisted nematic type simple matrix liquid crystal display device.

[0002]

2. Description of the Related Art Various types of liquid crystal display devices are used as display devices for office automation equipment. Such display devices require high-definition display, and therefore have a large number of pixels and high time-division driving. In addition, display characteristics are required to have high contrast and a wide viewing angle. In order to meet such demands, as a display device of a personal computer or the like, a super-twisted nematic type (hereinafter, referred to as STN type) liquid crystal display device capable of high time division driving and having relatively high contrast among liquid crystal display devices. A display device is used. This STN-type simple matrix liquid crystal display device includes a substrate disposed to face at a predetermined interval, an electrode disposed to intersect the inner surface of the substrate at right angles to each other, and an electrode forming surface. An alignment film formed so as to cover and align liquid crystal molecules in a predetermined direction, a liquid crystal material sealed between the alignment films, and disposed so as to sandwich the pair of substrates from outside the pair of substrates. And a pair of polarizing plates. The molecules of the liquid crystal material in the vicinity of the alignment film sealed between the alignment films are arranged in the alignment processing direction by the alignment regulating force of the alignment film, and the liquid crystal molecules are aligned on one substrate according to a predetermined alignment processing direction. And the other substrate is twisted at an angle of 180 ° to 270 °. The twist-aligned liquid crystal molecules change their orientation when an electric field is applied between the opposing electrodes by time-division driving, and the optical change accompanying this change in alignment is visualized by a pair of polarizing plates, so that the desired orientation is obtained. Is displayed. The above-described liquid crystal display device utilizes the birefringence effect of liquid crystal to increase the twist angle of the liquid crystal molecule arrangement in order to enable high time-division driving, and to increase visual contrast. There is a problem that the display is colored, and there is also a problem that the viewing angle is narrow and the display color changes depending on the viewing angle. To solve the problem of coloring described above,
A two-layer STN type in which a driving cell in which driving electrodes are provided on the opposing substrates as described above and a compensation cell in which the liquid crystal molecules of the driving cell are twisted in a direction opposite to the twist direction is arranged in two layers. Liquid crystal display devices have been proposed. The two-layer STN type liquid crystal display device can correct the difference in the phase difference for each wavelength light generated in the driving cell by the compensation cell,
Display close to black and white display can be achieved by suppressing the coloring of the display.

[0003]

However, the above-mentioned 2)
Since the STN type liquid crystal display device having a layer uses a liquid crystal cell similar to a driving cell as a compensation cell, the manufacturing process of the compensation cell is complicated and expensive, and the display device becomes large. There was a problem. Further, there has been a problem that the coloring of the display has not yet been sufficiently removed, and the viewing angle characteristics have not been improved. FIG. 8 shows an equal contrast curve in a conventional two-layer STN type liquid crystal display device. The isocontrast curves are 10 °, 20 °, 30 ° from the normal direction of the substrate of the liquid crystal display device.
The contrast when observed from directions tilted by 40 ° and 50 ° is shown in each direction. Here, a white triangle indicates a point having a contrast of 150, and similarly, a black triangle is 100, a white square is 50, a black square is 10, and a black circle is a point at which the contrast is negative, that is, a point at which the black and white display color is inverted. It shows. As is apparent from FIG. 8, the contrast of the front of the liquid crystal display device, that is, the normal direction of the substrate is 6
Although it is extremely high at about 00, the contrast is remarkably reduced as it is inclined from the normal direction. In particular, a region where the display color is inverted appears in the upper left and lower right directions of the liquid crystal display device, and the upper left inverted region is extremely large.
Therefore, in such a conventional liquid crystal display device, when viewed from a position inclined at an angle of 40 ° from the normal direction in the upper left direction, a negative image appears as a negative image, which is a very serious defect. . Also, FIGS. 9A, 9B, 9C,
In (D), the light transmission state (ON: ■) and light blocking when the liquid crystal display device is tilted by 10 ° from the normal direction of the substrate to 50 ° in each direction in the order of top, left, bottom, and right respectively. State (OF
The change in the display color of F: *) is shown on the CIE chromaticity diagram. Here, arrow b indicates the direction of chromaticity change of transmitted light in the ON state, and arrow a indicates the direction of chromaticity change of transmitted light in the OFF state. As is apparent from FIG. 9, ON and OF are set for each of the up, down, left, and right directions according to the inclination of the substrate from the normal direction.
The display color in the F state changes greatly. This is because the display color differs depending on the viewing direction of the liquid crystal display device,
The display quality was significantly reduced. The present invention has been made in view of the above circumstances, and has as its object to provide a liquid crystal display device having a simple structure and improved display coloring and viewing angle characteristics.

[0004]

In order to solve the above-mentioned object, in the liquid crystal display device of the present invention, an electrode which crosses each other and an alignment treatment is performed in a predetermined direction so as to cover the electrodes. And a pair of substrates on which the formed alignment films are formed, and sealed between these alignment films, twist-aligned in the range of 200 ° to 240 ° from one substrate toward the other substrate, and having a refractive index difference. The value Δnd of the product of the anisotropy Δn and the layer thickness d is 7
A liquid crystal material set in the range of 00 nm to 900 nm, and an alignment formed on a light-incident side substrate surface of the pair of substrates, the light-incident side of the pair of substrates being disposed on a side on which light is incident. A polarizer having a transmission axis direction set in a range of 135 ° to 180 ° with respect to the incident side alignment processing direction of the film; and a polarizer disposed on a light emitting side outside the pair of substrates; An analyzer in which the direction of the transmission axis is set in the range of 50 ° to 105 ° with respect to the orientation processing direction, and the product of the refractive index anisotropy Δn and the layer thickness d between the polarizer and the analyzer. Δnd of the liquid crystal layer is 0.9
１ ／ of the value multiplied by 0.95 and the incident side orientation
A first phase plate having a slow axis set in a direction of 15 ° to 110 ° with respect to the processing direction , and a product Δnd of refractive index anisotropy Δn and layer thickness d between the polarizer and the analyzer. Have substantially the same value as the first phase plate, and the slow axis is
Direction from -30 ° to 80 ° with respect to the processing direction , the light incident in a direction inclined from the normal direction of the substrate.
The slow axis of the first phase plate at an angle to correct the phase difference
And a second phase plate set in a direction that intersects the direction of . The first phase plate and the second phase plate are provided with the pair of bases.
On the outside of the board, sandwich each of these pair of substrates
Wherein the first phase plate is configured to be
Slow in the direction of 60 ° to 110 ° with respect to the side alignment processing direction
A phase axis is set, and the second phase plate is aligned with the incident side.
The slow axis is set in the direction of 30 ° to 80 ° with respect to the direction.
It is.

[0005]

According to the present invention, two phase plates are arranged between a polarizer and an analyzer of an STN type liquid crystal display device in which liquid crystal molecules are twisted by 200 ° to 240 °, and the retardation of these phase plates is performed. Since the relationship between the direction of the phase axis and the optical axis of the polarizer and the analyzer is set to the optimal condition, the difference in the phase difference for each wavelength light generated when the light passes through the liquid crystal cell becomes two phases. Substantially corrected by the plate, the coloring of the display color is eliminated. Also, 2
Since a plurality of phase plates are provided, the phase plate also corrects the phase difference from a direction inclined from the normal direction of the substrate, thereby reducing the inversion region and widening the region where high contrast can be obtained.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to FIGS. [First Embodiment] FIGS. 1 and 2 show an exploded perspective view and a sectional view of a first embodiment. In these figures, the liquid crystal cell 1
Is a lower substrate 4 on which one electrode 2 and an alignment film 3 covering the electrode 2 are formed, another electrode 5 crossing and facing the one electrode 2 and an alignment film 6 covering the other electrode 5 Are formed, a sealing material 8 for joining the upper and lower substrates 4, 7 at a predetermined interval, and a region surrounded by the upper and lower substrates 4, 7 and the sealing material 8, The value of the dielectric constant ratio {ε / ε} is 1.90, and the elastic constant ratio K3 / K1
Is 1.83, the value of K3 / K2 is 2.40, and the ratio d / p between the gap d and the natural pitch p is 0.5.

Light is incident on the liquid crystal cell 1 from below in the drawing. The lower substrate is hereinafter referred to as an incident side substrate 4 and the upper substrate is referred to as an outgoing side substrate 7. A polarizer 10 made of a linear polarizing plate is arranged outside the incident side substrate 4 of the liquid crystal cell 1, and an analyzer 11 made of a linear polarizing plate is arranged above the emission side substrate 7. Two phase plates 12 and 13 are provided between the emission side substrate 7 and the analyzer 11 of the liquid crystal cell 1.
Is arranged.

The alignment films 3 and 6 formed on the opposing surfaces of the incident side substrate 4 and the outgoing side substrate 7, respectively, are subjected to an alignment treatment such as rubbing.
As shown in FIG. 1, when the liquid crystal cell 1 is observed from the front, an alignment process is performed in a direction 3a having an inclination of about 30 ° from the lower left to the upper right with respect to a horizontal line. The orientation film 6 of the emission-side substrate 7 facing the incidence-side substrate 4
In the clockwise direction (hereinafter, referred to as negative or-) with respect to the alignment direction 3a (hereinafter, referred to as the incident side alignment direction).
The orientation processing is performed in the direction 6a rotated by °. By such an alignment treatment, the molecules of the liquid crystal material are aligned at a pretilt angle of about 8 °, and are arranged as a 240 ° (φo) twist in the negative rotation direction from the incident side substrate 4 to the emission side substrate 7. The value of the product △ nd of the gap d and the refractive index anisotropy △ n of the liquid crystal cell 1 is 864 nm (measurement wavelength: 5
89 nm).

The polarizer 10 has its transmission axis 10a disposed in a + 140 ° (α) direction counterclockwise (hereinafter referred to as positive or +) with respect to the incident side alignment processing direction 3a. The transmission axis 11a is arranged in a direction intersecting the incident side alignment processing direction 3a at 55 ° (ε).

The first and second phase plates 12 and 13 are phase plates obtained by uniaxially stretching polycarbonate and having a value of Δnd of 400 nm (measurement wavelength: 589 nm). The value of Δnd that is smaller by the amount corresponding to the decrease (0.
90 to 0.95 times). First phase plate 1
The second phase plate 1 has its slow axis 12a arranged in a direction of approximately + 40 ° (β) with respect to the incident side alignment direction 3a.
3 almost its slow axis 13a is to the incident-side aligning treatment direction 3a - is arranged 5 direction ° (gamma).

The STN-type liquid crystal display device having the above-described structure has the following features.
The difference in the phase difference for each wavelength light generated when the light passes through the liquid crystal cell 1 is substantially corrected by the two phase plates 12 and 13,
The coloring of the display color is eliminated, and the two phase plates 12, 1
3, the phase difference from the direction inclined from the normal direction of the substrate is also corrected, the inversion area is reduced, and the area where high contrast is obtained is widened.

FIG. 3 shows each contrast curve of the present embodiment. This isocontrast curve diagram is 10 °, 20 °, 30 °, 40 °, and 10 ° from the normal direction of the substrate of the liquid crystal display device.
And the contrast when observed from a direction inclined by 50 ° in each direction. Here, a white triangle represents a point with a contrast of 150, and a black triangle represents 1 point.
00, a white square represents 50, a black square represents 10, and a black circle represents a point where the contrast becomes negative, that is, a point where the black and white display color is inverted.

According to FIG. 3, as compared with the conventional liquid crystal display device shown in FIG. 9, the range in which the contrast 10 can be obtained is wider, the inversion region appearing above the liquid crystal display device is reduced, and No inversion area appears below the liquid crystal display. Therefore, according to the present embodiment, it is clear that the viewing angle is widened and the viewing angle characteristics are improved.

FIGS. 4A, 4B, 4C, and 4D show:
The light transmission state when the liquid crystal display device is tilted by 10 ° from the normal direction of the substrate to 50 ° in order of upper direction, left direction, lower position, and right direction in each order (ON: black square)
And the change of the display color in the light blocking state (OFF: *) is shown on the CIE chromaticity diagram. Here, an arrow a indicates a change in chromaticity of transmitted light in an ON state, and an arrow b indicates a change in chromaticity of transmitted light in an OFF state. As is clear from FIG.
Compared with the conventional liquid crystal display device shown in FIG. 9, there is little change in display color for each direction.

As in this embodiment, two phase plates 12 and 13
Are arranged adjacent to each other, and the twist angle φ of the liquid crystal of the liquid crystal cell 1 is
When o is in the range of 200 ° to 240 ° and △ nd is in the range of 700 nm to 900 nm (measurement wavelength: 589 nm), the polarizer 10
The angle α of the transmission axis 10a is in the range of 135 ° to 180 °, and the angle ε of the transmission axis 11a of the analyzer 11 is 40 ° to 1 °.
The slow axis 12a of the first phase plate 12 is set to (2
70 ° − | φo |) ± 15 °, the second phase plate 13
The slow axis 13a of (270 ° − | φo | / 2) ± 15 °
And the first and second phase plates 12 and 13
It is desirable to multiply the value of △ nd of the liquid crystal cell 1 by the value of △ nd of the liquid crystal cell 1 by a value of 0.90 to 0.95, and divide this by the number 2 of phase plates.

[Second Embodiment] A second embodiment will be described with reference to FIG.
This will be described in detail with reference to FIGS. In the second embodiment, a first phase plate and a second phase plate are arranged on both sides of a liquid crystal cell, and the same members as those in the first embodiment are denoted by the same reference numerals and are described. Omitted. In FIG. 5, a polarizer 10 made of a linear polarizing plate is arranged below the incident side substrate 4 of the liquid crystal cell 1, and an analyzer 11 made of a linear polarizing plate is arranged above the emission side substrate 7. I have. A first phase plate 12 is arranged between the incident side substrate 4 and the polarizer 10 of the liquid crystal cell 1, and a second phase plate 13 is arranged between the emission side substrate 7 and the analyzer 11.

The alignment direction of the alignment film of the liquid crystal cell 1 and the alignment state of the liquid crystal material are the same as in the first embodiment.
The transmission axis 10a of 0 is + 145 ° (α) counterclockwise (hereinafter referred to as positive or +) with respect to the incident side alignment processing direction 3a.
The transmission axis 11a of the analyzer 11 is disposed at + 70 ° (ε) with respect to the incident side alignment processing direction 3a.

The first phase plate 12 has its slow axis 12a disposed in a direction of approximately + 85 ° (β) with respect to the incident side alignment processing direction 3a, and the second phase plate 13 has its slow axis 13a They are arranged in a direction of approximately 40 ° (γ) with respect to the orientation processing direction 3a.

In the above-described STN type liquid crystal display device of the second embodiment, as in the first embodiment, the phase difference of each wavelength light generated when the light passes through the liquid crystal cell has two phase plates. Is almost corrected, the coloring of the display color is lost, and 2
The phase difference from the direction inclined from the normal direction of the substrate is also corrected by the two phase plates, and the area where high contrast is obtained is wide.

FIG. 6 shows an equal contrast curve of this embodiment. This isocontrast curve diagram is 10 °, 20 °, 30 °, 40 °, and 10 ° from the normal direction of the substrate of the liquid crystal display device.
And the contrast when observed from a direction inclined by 50 ° in each direction. Here, a white triangle represents a point with a contrast of 150, and a black triangle represents 1 point.
00, a white square represents 50, a black square represents 10, and a black circle represents a point where the contrast becomes negative, that is, a point where the black and white display color is inverted.

According to FIG. 6, as compared with the conventional liquid crystal display device shown in FIG. 8, the range where the contrast 10 can be obtained is expanded in the horizontal direction. Therefore, according to the present embodiment, the viewing angle characteristics are improved.

FIGS. 7A, 7B, 7C, and 7D show:
The liquid crystal display device has an upper direction, a left direction, a lower position, and a right direction in the order of 50 ° in order of 10 ° from the normal direction of the substrate for each direction.
The change in the display color between the light transmitting state (ON: black square) and the light blocking state (OFF: *) when tilted up to ° is shown on the CIE chromaticity diagram. Here, an arrow a indicates a change in chromaticity of transmitted light in an ON state, and an arrow b indicates a change in chromaticity of transmitted light in an OFF state. As is clear from FIG. 7, in the present embodiment, the change of the display color in each direction in the OFF state is smaller than in the conventional liquid crystal display device shown in FIG.

As in the present embodiment, the two phase plates 12 and 13
Are disposed at both ends of the liquid crystal cell 1, the twist angle φ0 of the liquid crystal of the liquid crystal cell 1 is 200 ° to 240 °, and the value of Δnd is 70.
When the wavelength is in the range of 0 nm to 900 nm (measurement wavelength: 589 nm), the angle α of the transmission axis 10a of the polarizer 10 with respect to the incident side alignment direction 3a is 135 ° to 180 °.
The angle β of the slow axis 12a of the first phase plate 12 is set in the range of (180 ° − | φ0 | / 2) to (180 ° − | φ0 |
/ 2) the slow axis 13 of the second phase plate 13 within the range of + 30 °.
The angle γ of a is 180 ° − | φ0 | / 2) to (180 °
− | Φ0 | / 2) −30 °, and multiplying the value of Δnd of the first and second phase plates by the value of 0.95 to 0.95 to the value of Δnd of the liquid crystal cell. Is preferably set to a value obtained by dividing by the number 2 of the phase plates. That is, the angles α, β, γ, and ε are 140 ° to 180 °, respectively.
60 ° to 110 °, 30 ° to 80 °, 50 ° to 9
It is desirable to set it in the range of 0 °.

As described above, according to the present invention, the polarizer 10 and the analyzer 11 arranged with the liquid crystal cell 1 interposed therebetween with reference to the incident side alignment processing direction 3a of the STN type liquid crystal cell 1.
Angles α and ε of the transmission axes 10a and 11a, and a first phase plate 12 disposed between the polarizer 10 and the analyzer 11;
The angles β and γ of the slow axes 12a and 13a of the second phase plate 13 are 135 ° to 180 °, 40 ° to 105 °, respectively.
By setting the angle in the range of 15 ° to 110 ° and -30 ° to 80 °, the viewing angle characteristics and the coloring of the display can be improved.

In the present invention, an example is shown in which the first phase plate 12 and the second phase plate 13 are formed of a phase plate made of polycarbonate. However, the present invention is not limited to this, and polyvinyl alcohol is sandwiched between protective films. A phase plate may be used.

[0026]

According to the present invention, the liquid crystal is moved from 200 ° to 240 °.
In an STN-type liquid crystal display device including a twist-aligned liquid crystal cell and a pair of polarizing plates sandwiching the liquid crystal cell, two phase plates are further disposed between the polarizing plates, and each optical axis is optimized. Since the conditions are set, the viewing angle characteristics of the liquid crystal display device are wide, and the coloring of the display is reduced.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing a schematic configuration of a first embodiment of the present invention.

FIG. 2 is a sectional view showing a first embodiment of the present invention.

FIG. 3 is an equal contrast curve diagram in the liquid crystal display device of the first embodiment.

FIG. 4 is a CIE chromaticity diagram showing a change in display color in the liquid crystal display device of the first embodiment.

FIG. 5 is an exploded perspective view showing a schematic configuration of a second embodiment of the present invention.

FIG. 6 is an equal contrast curve diagram in the liquid crystal display device of the second embodiment.

FIG. 7 is a CIE chromaticity diagram showing a change in display color in the liquid crystal display device of the second embodiment.

FIG. 8 is an equal contrast curve diagram in a conventional liquid crystal display device.

FIG. 9 is a CIE chromaticity diagram showing a change in display color in a conventional liquid crystal display device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 liquid crystal cell 2, 5 electrode 3, 6 alignment film 4 incident side substrate 7 emission side substrate 8 sealing material 9 liquid crystal material 10 polarizer 11 analyzer 12 first phase plate 13 second phase plate 3 a, 6 a rubbing direction 10 a, 11 a Transmission axis 12a, 13a Slow axis

Claims (3)

(57) [Claims] 1. A pair of substrates, each having an intersecting electrode and an alignment film covering the electrodes and having been subjected to an alignment treatment in a predetermined direction, on each of the opposing surfaces, and between the alignment films. And 200 from one substrate to the other substrate
Twisted in the range of ° to 240 °, and the value Δnd of the product of the refractive index anisotropy Δn and the layer thickness d is 700 nm to 90 nm.
A liquid crystal material set in a range of 0 nm, and an alignment film formed on a light-incident side substrate surface of the pair of substrates which is disposed on a side where light outside the pair of substrates is incident. The direction of the transmission axis is set to 1 with respect to the incident side alignment processing direction.
A polarizer set in the range of 35 ° to 180 °, and a polarizer disposed on the side where light outside the pair of substrates is emitted, and having a transmission axis direction of 50 ° to 105 ° with respect to the incident side alignment processing direction. ° and a value Δn of the product of the refractive index anisotropy Δn and the layer thickness d between the polarizer and the analyzer set in the range of °.
d is の of the value obtained by multiplying the value of Δnd of the liquid crystal layer by 0.9 to 0.95, and is 15 with respect to the incident side alignment processing direction .
Between the polarizer and the analyzer, the product Δnd of the refractive index anisotropy Δn and the layer thickness d is the first phase plate And the slow axis is-with respect to the incident side alignment processing direction .
30 ° to 80 ° direction, the normal direction of the substrate
Corrects phase difference for light incident in the direction inclined from
A liquid crystal display device comprising: a second phase plate set at an angle in a direction intersecting the direction of the slow axis of the first phase plate . 2. The first phase plate and the second phase plate, wherein the first phase plate and the second phase plate
Outside the pair of substrates, sandwich the pair of substrates.
The arrangement according to claim 1, wherein the respective arrangements are arranged.
Liquid crystal display device. 3. The method according to claim 1, wherein the first phase plate is provided on the incident side.
The slow axis is set in the direction of 60 ° to 110 ° to the direction.
And the second phase plate is oriented with respect to the incident side alignment processing direction.
The slow axis is set in the direction of 30 ° to 80 °
The liquid crystal display device according to claim 2, wherein: